Purpose: :
In vivo confocal microscopy (IVCM) has recently enabled elucidationof the 2-dimensional structure of the corneal sub-basal nerveplexus. However, acquiring a full montage of the cornea is atime consuming process: a typical map requires many hundredsof images. The purpose of this work was to develop and testa system for semi-automated montaging of images taken of theliving human corneal sub-basal nerve plexus.

Methods: :
Software was developed to process a complete set of IVCM imagesfrom a normal living human cornea. A preprocessing step removedimages containing unwanted features such as epithelium. Forthe remaining images, keypoints were generated that encodedlocal branching information. That information was used to generatea potential stitch between pairs of images using the RANSACalgorithm. Image based criteria were applied to decide whetheror not the stitches were valid. The resulting adjacency informationyielded groupings of overlapping images. Semi-automated meanswere employed to allow the inclusion of image matches that werebelow threshold, as well as possible matches with rejected images.The resulting automated montages were compared against two previouslymanually stitched montages, constructed from a total pool of640 and 373 images respectively.

Results: :
Over 71% of all images were accepted for stitching, with >87%sensitivity and <37% specificity. The low specificity occurredas redundant images had been eliminated from the manually stitchedmontages. Potentially mismatched images (false positives) weredetected (<1.5%), but these were traced to errors in themanually created montages. The adjusted false positive ratewas therefore zero in both instances. The final montages bothcontained 61 groups. Two large groupings were found in eachexample, containing 68% and 50% of accepted images (367 and166 images respectively). Unmatched images comprised <11%of all groups. The semi-automated process of adding image pairsmanually accounted for <29% reductions in the number of groups.Processing times for these examples were 2 hr 24 min. and 1hr 7 min., without optimization.

Conclusions: :
The majority of accepted images were matched (>89%), halfor more were collected into a single group. The semi-automatedresult agreed with a manually stitched montage. In fact someerrors in the latter were revealed by the comparison. Semi-automatedstitching will be a useful, effective and time saving tool forfurther studies involving corneal nerve imaging by IVCM. Furtherwork will aim to extend and optimize the methods developed here.